souphttpsrc: add cookie jar
Submitted by Eunhae Choi
In case of adaptive streaming, there is a additional http src element in the adaptive demux to download content fragments.
In some cases, user-agent and cookie is needed to set to connect the http server but there is no way to get the current user-agent and cookie data from souphttpsrc.
I think souphttpsrc should handle the custom query of user-agent and cookies.